This invention relates to unsaturated polyester molding compounds having improved impact resistance and good surface appearance.
Unsaturated polyesters are well known. They may be prepared, for example, by condensing an ethylenically unsaturated dicarboxylic acid or anhydride with a dihydric alcohol.
Unsaturated polyesters are conventionally used in molding compounds in combination with an unsaturated monomer which is polymerizable with the polyester. The unsaturated monomer participates in the crosslinking of the composition during the curing reaction. Molding compounds which contain only an unsaturated polyester and an unsaturated monomer usually exhibit poor surface gloss and are prone to shrinkage during curing. Furthermore, these compounds typically exhibit poor impact strength.
Additives have therefore been developed to reduce the shrinkage and improve the surface appearance of moldings prepared from unsaturated polyesters. Similarly, additives have also been developed to improve the impact strength of these compounds.
Certain thermoplastic additives are particularly suitable to improve surface appearance and reduce shrinkage. For example, U.S. 3,701,748, to Kroekel, teaches the use of from 1 to 25 parts of a "thermoplastic polymer" to improve the surface of moldings made from unsaturated polyesters.
U.S. Pat. No. 3,998,909, to Roberts et al., teaches the use of a "thermoplastic composition" to improve the surface characteristics, including shrink and gloss, of molded thermosetting resin compounds.
U.S. Pat. No.4,096,102, to Strauss et al., teaches the use of "thermoplastic additives" to reduce the "shrinkage on molding" of unsaturated polyester resins.
Thus, the use of thermoplastic additives in unsaturated polyester molding compounds is well known.
Similarly, certain elastomeric additives are particularly suitable to help improve the impact strength of moldings made from unsaturated polyesters.
U.S. Pat. No. 3,857,812, to Nowak et al., teaches the use of from 5 to 15 parts of a "polydiene rubber" having a specified viscosity and molecular weight as an additive in a thermosettable compositoin suitable for preparing impact resistant plastic articles.
U.S. Pat. No. 3,577,478, to Thorpe, teaches a blend of a polymer of butadiene with an unsaturated polyester compound to prepare a blended product with high impact strength.
U.S. Pat. No. 4,336,344 to Craigie, teaches the use of a combination of a carboxy terminated polydiene rubber and a triblock polymer "compatibilizing agent" as an additive to unsaturated polyester molding compounds.
U.S. Pat. No. 4,160,759, to Gardner et al., teaches the use of a "conjugated diene butyl rubber" as an additive in a polyester molding compound having improved impact strength. It is also significant to note that Gardner also teaches the preferred use of a further thermoplastic polymer additive.
Thus, the use of elastomeric additives in unsaturated polyester molding compounds is well known.